Hi,

What is the reason for this prompt "Camera Parms are not writable!" ?

Thanks.

likely because you are looking through camera of the Display flagged node, which doesn't have those parms
drag your camera1 node into the viewport, the path will display testgeometry_rubbertoy1/camera1:cam1 then editing through viewport will try to edit the testgeometry_rubbertoy1/camera1 node which does have those parms and should work